The present invention relates to a heat exchanger which is intended to be applied onto a subject""s body for controlling the subject""s body temperature during medical procedure.
There are a variety of medical procedures in which a subject""s body temperature has to be controlled. For example, during open heart surgery, the body temperature has to be controllably reduced to about 35xc2x0 C. and then at the end of the operation increased back to normal body temperature. Furthermore, under general anesthesia, the natural physiological mechanisms which operate to maintain a body temperature may fail, and the problem becomes particularly acute in cases where exposed internal body organs come into contact with the ambient air which results in excessive heat loss. The problem is further aggravated by the fact that operation rooms are very often heavily cooled. Following surgical procedure, it may take some time until the body acquires back its ability to control its temperature.
Similarly as human subjects, the problem of controlling body temperature is also experienced during surgical procedures performed on animals.
Overall, controlling the body temperature is one of the serious problems facing the medical staff when performing operations.
U.S. Pat. No. 4,844,072, describes a system which may be used in thermal therapy and which includes a thermal pad with internal channels for carrying a temperature-control liquid therethrough. A thermal bandage which achieves a similar purpose is described in U.S. Pat. No. 4,962,761 through which heat control liquid is circulated when placed in contact with the body. In accordance with this patent, several such matters may be placed in series and fitted into a planar array or into a garment.
U.S. Pat. No. 5,269,369 discloses a temperature regulation system for human body which makes use of heat pipes which are incorporated into a garment, which distributes energy to and from portions of the human body.
A tube laminated heat transfer article for placing against a human body for transfer heat to or from the human body is disclosed in U.S. Pat. No. 5,755,275. A heating and/or cooling pad having the shape of the human body which is placed beneath the patient to allow heat or cold to radiate upwards is disclosed in U.S. Pat. No. 5,785,716.
MicroClimate Systems Inc., Stanford, Mich., U.S.A., markets a series of portable personal cooling systems (sold under the trademarks KOOLVEST, KOOLJACKET, KOOLBAND, KOOLPAID and others) which are intended for use by healthy persons who perform a physical activity in a hot environment (see Internet http://www.microclimate.com/prodline.html or http://www.microclimate.com/work.html). The system consists of a garment (it may be a vest, jacket, skull cap, a cervical collar, etc.) with tubing embedded therein in which water flows propelled by a battery-powered pump. Water passes through ice or through a cooling device before entering the tubing within the garment. The user can control the pump rate, the temperature, etc. A similar product line is also provided by Mallinckrodt Inc., St. Louis, Mo., U.S.A. (see the Internet at http://www/mallinckrodt.com/ccd) and others.
In accordance with the invention, a heat exchanger in the form of a garment which is highly effective in transferring a heat to or from a subject""s body in order to control the subject""s body temperature has been developed. The invention thus provides, a heat exchanger for use in controlling a subject""s body temperature during a medical procedure, comprising:
a flexible garment adapted for enveloping portions of the subject""s body surface, the garment having dedicated sections for enveloping different body parts which comprise a torso section for enveloping substantial portions of the subject""s torso and one or more extremity sections for enveloping portions of one or more of the individual""s extremities;
a fastening arrangement for retaining each section in an enveloping state;
fluid-tight space defined between an internal, body-facing layer of the garment and an external layer and between fluid tight edges of the garment, the faces of both layers lining said space being attached to one another along lines defining a flow path between at least one fluid inlet and at least one fluid outlet to permit flow of fluid from the at least one inlet to the at least one outlet throughout essentially the entire garment for effective heat transfer to or from all parts of the garment;
the inner faces of the garment""s internal and external layers are made of a heat-weldable material and are point welded to one another at a plurality of locations throughout the garment.
The fluid-tight space which is defined between the internal and the external layers of the garment, has typically a volume per unit area which is essentially the same throughout the entire garment. The point welds may be randomly distributed throughout the garment or may be arranged in an ordered array. A typical distance between two adjacent welded points in the garment is between about 8 to about 20 mm.
The garment is typically designed for working under fluid pressure of about 0.5-1.5 atmospheres. Typically, the space is formed such that under a pressure of this range the space""s volume per unit area of the garment is in the range of about 1-3 liter/m2 of garment surface.
A preferred heat exchanger in accordance with the invention is such wherein each of the internal and the external layers is constructed of two layers; namely the garment is a four-layered structure. This four-layered structure consists of two impermeble sheets lining said space overlaid by usually heavier reinforcing layers. All four layers are typically made of a heat-weldable material and are point welded to one another. The two innermost layers serve to define the fluid-tight space, while the outer layers reinforce the structure and allow the application of an increased internal fluid pressure, at times up to about 3 Atm without rupturing. Increase pressure may at times be of importance to ensure a certain level of flow of the heat-control fluid within the garment""s inner space. The inner layers of the heat exchange may be made of a polyethylene-based material such as Metallocene (manufactured by Dow Chemicals) sheeting, typically but not restricted to about 20-50 xcexcm thickness. The two outer layers are preferably somewhat hydrophilic to allow a certain degree of absorption of body and/or cleaning and disinfecting fluids and are also preferably soft to touch to ensure improved patient""s comfort when contacting the skin. The outer layers may, for example, be made of a woven or non-woven spunbond fabric, e.g. made of polypropylene, having a characteristic weight of about 20 g/m2 to about 50 g/m2. The welding together of the four layers may be achieved, for example, by means of RF welding.
The heat exchanger having the aforementioned characteristics, is novel by itself (even when not formed into a garment as defined above), and forms an aspect of the present invention. The heat exchanger may be used for any application requiring a flexible heat exchanger with a relatively large heat exchange surface. A significant feature of the heat exchanger of this embodiment is that it is of low cost and high efficiency and has overall performance (heat exchange properties, flexibility, internal pressure resistance, and others) hitherto attained only with more complex and costly devices.
The heat transfer fluid is typically a liquid, e.g. water. A heat exchanger which is adapted for use with a liquid heat transfer fluid, typically made to circulate by a pump, is made with an internal flow resistance within the space such that under a pressure differential between the input and output of about 0.5 atmospheres, the flow rate through the garment will be in the range of about 0.5-2 liter/minute, typically about 1 liter/minute.
The garment is preferably designed such that each different section can be manipulated independently from other sections between an enveloping and a non-enveloping state. This has several advantages. For one, it allows easy accessibility to different parts of the body. Furthermore, this allows to use a single type of garment for different kinds of operations: for example in case of an operation performed on the subject""s leg, the respective section will obviously be in the non-enveloping state while the other sections, namely those of the torso, the other leg, the arms, the neck, the head, etc., may be in an enveloping state. The feature of independent manipulation of the different sections between an enveloping and a non-enveloping state is typically achieved by emarginations in the garment""s edges.
The garment may also have a modular design. For example, there may be a garment piece designed for the torso, a garment piece designed for the head, a garment piece designed for the legs or arms, etc. The different garment pieces may be combined to form a garment in a manner to meet specific needs.
The above feature allows to provide an effective cover of the human body by the garment sufficient to properly control the body temperature, for a wide variety of different medical procedures. One should also note that. effective heat transfer may be achieved regardless of the patient""s position: whether he is placed lying on his back or whether he is placed with his back up or whether he is placed lying on his side, or even when positioned in a sitting position.
The heat exchanger of the invention is particularly useful in controlling the body temperature of a patient during surgery. The heat exchanger in accordance with the invention may be designed for all shapes and sizes of human subjects as well as for animals.
The invention will now be described in a non-limiting manner with respect to some specific embodiments shown in the annexed drawings.